Antihunting temperature sensitive detector



Feb.26, 1952 J. A. ROBERTS ANTIHUNTING TEMPERATURE SENSITIVE DETECTOR 2 SHEETS-SHEET l Ivento 'En A, Roberts,

Hi8 Attorwney.

Feb. 26, 1952 Filed Dec,

pig 4. i

J. A. ROBERTS ANTIHUNTING TEMPERATURE SENSITIVE DETECTOR 2 SHEETS-SHEET 2 Hl GH TEMPERATURE,

L 0W TEMPERATURE.

Inventor; Jol'n A. Roberts,

His Attov'wfwey.v

Patented Feb. 26, 1952 ANTIHUNTINGA TEMPERATURE SENSITIVE DETECTOR John A. Roberts, East Lynn, Mass., assignor to General ElectricA Company, a-corporation of New York Application December 15, 1949, Serial N o. 133,169l

(Cl. 'I3-352) 4 Claims.

My invention relates io a temperature sensi tive detector ofthe type employing a bimetallic contact device which opens and closes a 'signal circuit as the temperature of the bimetal varies between predetermined limits, and it is the object of my'invention to improve the operation of such l l devices by reducing the hunting tendency and contact sticking in such devices.

In carrying my invention into effect, I superimpose upon the thermal responsive vibratory action of the contact mechanism an electromagnetic vibratory action of a frequency much higher than that of the thermal responsive vibratory action, such that the normally slow, variable pulse rate of the contact device is changed to a higher constant frequency pulse rate. The resultant root mean square value of the current which is passed by the contacts is not changed by reason of my invention, but th-e detector action is much smoother and results in other advantages as will be explained.

The features of my invention which are believed to be novel and patentable will be pointed out in the claims appended hereto. For a better understanding of my invention reference is made in the following description to the accompanying drawing in which Fig. l represents an enlarged view of a temperature measuring detector embodyingmy invention with the enclosing case shown in section. Fig. 2 represents a wiring diagram of a complete temperature measuring system to which my invention is applied. Fig. 3 is a cross-sectional detail of Fig. 1. Fig. 4 represents comparative oscillograph records of the current through the contacts of temperature responsive devices before and after being vequipped with -my antihunt regulator.V Fig. 5

represents a pressure measuring detector employing my invention.

Referring now to Fig. 1, I represents a stainless steel casing of circular cross section of a temperature sensitive detector probe having a sharpened end 2 to enable the probe to be insertedl into a roast of meat, for example, for the purpose of determining its internal temperalture. Theother end of the probe casing is tems porarily left open for the insertion of a chromeiron sleeve 3 which supports within it a pair of conductor wires 4 and 5 insulated from each other and from the sleeve 3 by insulating supporting structure including a glass bead seal `l which forms an airtight partition across the sleeve 3. The conductor 4 is to be magnetic, and I have found it convenient to make both con'- ductors 4 and 5 from a commercially available ycopper covered iron wire. v

The forward end of wire 4 serves as a magnetic pole piece I and the Wire is electrically connected to the adjacent end of a coil 8 wound about the wire 4 adjacent the pole end 'I of the wire 4. The other end' of coil B is connected to lead-in wire 5 and, of course, the coil 8 is suitably insulated between its turns and from wire '4. Welded or otherwise secured to wire 4 closely adjacent the rear end of coil 8 is a spring steel reed 9 which has on its free end a magnetic pole shoe 9a in ymagnetic armature nrelation with the pole l. The length of the electromagnet and armature thus formed may be about one inch and otherwise proportional about as illustrated. and the free air gap spacing between the armature 9a and pole I may be about-0.01 inch. Onjthe i same side of the end of armature reed 9 as pole 'I is a contact button I0 which cooperates with a contact button II on the free end of a temperature sensitive bimetallic contact spiral I2 havingr its other end electrically and mechanically secured to an extendingportion of sleeve 3 as by a tap I3 of spring steel which seems to protect the bimetal spiral from shock. The bimetal contacter spiral I2 is arranged to turn away from contact Ill Iupon an increase in temperature above a predetermined value and.. to close on contact IIJ at and below such predetermined temperature when the contact I0 is mits free nonvibrating condition. The normal temperature at which the contacts I0, I I Will separate is readilyA adjusted to the desired value as by bending the tab I3.

The electromagnetic vibrator and bimetallic contactor parts just described are assembled and adjusted, and the assembly sealed in and to the sleeve 3 prior to inserting the sleeve into the casing I. A hollow metallic tube. I4 may be inserted into an indentation along one edge of sleeve 3 near the head end thereof in a manner best shown in Fig. 3. The sleeve with the parts thus assembled is then inserted into the open rear end of tube I. A flanged head piece I5 is then added as shown in Fig. l, and the sleeve 3', tube I4 and head piece I5 are all silver soldered together and to casing I at its open end as indicated at I6, so that the electromagnet and bimetal contact parts are now contained in an airtight compartment, except for a metal tube I4, sealed by such silver solder I6 and by the glass bead 5. The tube I4 may now beused to evacuate such chamber and to introduce any f i length and may be used as the electrical connection to the tab end of bimetallic arm I2 through metallic sleeve 3. A closure cap II is provided to be permanently or removably secured over the head piece I5, and these parts will be provided with an opening for the entrance of a suitablyvprotected cable I3 for the lead-in wires. The lead-in wires are welded to the exposed ends of conductors ii, 5 and I4 before the cap I'I is added. Where a metal armored cable is used, the sheath thereof may be used asv the conductor to the sleeve 3 and be brazed to the flange I5. So far as the main feature of my invention is concerned, the structural details of the probe may vary considerably from those above described. The unoccupied space in the head I5-I'I may be filled up'with an insulating packing.

`A suitable electric circuit for the apparatus when used for measuring temperature is illustrat'ed in Fig. 2, where I9 represents a standard 11-0-volt, 60-cycle source of supply, and 20 a stepdo-wn transformer such as will give about ve volts from its secondary. The contacts I and I I are connected across this 5-volt source of supply through an ammeter 2|. The electromagnetic coil S is also connected across the 5-volt source of supply. The current of such coil 8 does not pass through the amnieter.

If the electromagnet comprising coil 8, its magnetic core 4, and armature il were omitted or if the coil 8 were disconnected so that contact Il) would remain stationary, the operation of the apparatus would correspond to known tempera-Y y ture measuring apparatus and would function as follows. The probe or that part thereof surrounding its bimetal contact device is located at the point or area where the temperature is to be measured. It is adjusted so that the contacts are closedrat or slightly below the lowest temperature to be measured. A certain value of current thus flows through the ammeter and through the bimetal I2 at such temperature. This current heats the arm I2 (or a separate heater through which the current flows heats the arm), and also the current causes a maximum deection of the ammeter.

YAt such minimum temperature the heat carried away from bimetal I2 to the Vsurrounding area is just sufficient to prevent opening of the contacts, and the full-scale deflection of the instrument is calibrated or marked with such minimum temperature value. Now', when the temperature to bemeasured rises, less heat is 'conveyed away from l2 and it thus flexes and opens the contacts. This cuts olf its own'heating and it cools and vcloses the contacts, and this action is repeated. The higher the temperature to be measured, the lower will be the laverage current through I2 that is necessary to reopen the contacts. As thel temperature to be measured "increases, the pulse rate 'decreases and the con'- tacts 'remain open a largervpor'tion of the time. rl-Ience, a correspondingly smaller average current flows through theammeter. The *ammeter is of va type which has considerable damping andpreferabl'y, also, of `a type which is designed to measl ure the root mean square value of the current4 y flowing. Hence, the ammeter tries to average the root mean square value of the current pulses and has a deflection less than the original value by an amount which is proportional to the heat "supplied by the current to l2 whichis lnecessary to "keep `the contacts Vfrom 'remaining closed. This reduction in instrument deflection is proportional to the temperature to be measured and, hence, the ammeter scale may be calibrated in terms of the temperature to be measured.

Representative pulse rates of such prior art devices when operating satisfactorily vary between two and eight pulses per second. At the higher measurement temperatures when the pulse rate is slow, there is considerable flickering of the ammeter pointer even in a well damped instrument. Also, at all temperatures the breaking action at the contacts tends to cause sticking and freezing of the contacts, which augments the diic'ulty and shortens the useful life of such contacts.

According to my invention the contact li), which in comparable prior art deviceswas normally stationary, is vibrated at a high rate of speed, in the example given, at' 120 times per second, by the vibrator'electromagnet which vibrates reed armature 9 once for each half cycle of the (iO-cycle alternating current supply.

When the electromagnet is energized on the positive and negative half waves of the altere nating current, the reed armature 9a is attracted toward pole l, and contact I0 moves toward contact Il, and as the alternating current reverses and passes through zero value, the reed 9 springs away from pole 1, and its contact I0 moves away from contact Il. As a result of this vibration of contact l0, the contacts I0 and II instead of remaining closed for several cycles and then open for several cycles, remain closed for only a fraction of each half cycle and open for the remainder of each half cycle, and the fraction of time per half cycle o contact closure is inversely proportional to the temperature to be measured. The average amount of heating current supplied to the bimetal spiral I2 and the average amount of heating furnished are the same as before, but the current pulses are broken up into a very much larger number of smaller pulses, and the pulse rate instead of being variable is constant.

Also, I preferably design the vibratory reed contact device so that the contacts will generally open at or near the zero part of the alternating current wave. For use on a 60-cycle supply and where energization of the electromagnet moves its contact towards closing position. I may design the reed so that it will have a Ynatural period of vibration somewhat higher than the 7200 .per minute pulsation rate of the frequency. Thus, if the `reed is designed so that it has a natural period of vibration of around 8000 cycles per minute, its phase will tend to lead that of the alternating pulsations and will tend to open the vcontacts near the zero value of the alternati'g current through the contacts. ThisLof course, assumes that the electromagnet which vibrates the reed is supplied from the same valternating current source which supplies the circuit through the contacts, which is the case in the arrangement described. This tuning of the reed, however, is not essential to my invention because the vibratory action will provide a quick make and break of thecontacts and-minimizes any tendency yof the contacts to -arc and become welded to'- 4gether.

The difference in the operation Abefore and after applying my invention is illustrated-in the records of Fig. 4. Records A and -A are approximate reproductions of Voscillograpli records of the current through the bimetal of a tem'- `p'erature sensitive'detector'at high and low temperatures respectively where Athe detector does not have any improvement, and records B and B are corresponding records under similar con-V ditions after my invention has been added. The central line of each record represents zero current, the portions above such line the positive portions of a cycle, and the portions below such line the negative portions of a cycle. VIn records A and A it is noted that when current flows, it flows at full value during one or more cycles and the pulse rate varies from a condition at high temperature where the contacts are4 closed during about'one cycle with a full open period of many cycles, to a condition where the contacts are closed for several cycles and an open period of several cycles at low temperatures. With my invention,.curve B, the pulse rate is constantl at 120 cycles per second, but the current flow per cycle varies substantially uniformly in inverse proportion to the temperature to be measured.

Itis evident thatv afcurrent measuring instru. ment, such as the instrument of Fig. 3, will be able to average thecurrent of curve B without fluctuation between pulses, while the irregular pulses of curve A will cause fluctuation in the averaging measurement. Equally important is the fact that the vibratory action present inmy improved detector prevents sticking and freezing of thecontacts, -while the conditions present in the type of operation represented by curve A are favorable to sticking and freezing of the contacts. This means that a detectorequipped with my invention will have a longer trouble-free life than one without such improvement. The damping requirements ofthe' measuring instrument used become much less exacting with my invention.

In Fig. 5 my invention is shown as asI applied to a pressure measuring thermal type of detector. The parts corresponding to those prefV viously described are identified by similar reference characters. The magnetic wire 4 is shown mounted upon the under side of a flexible diaphragm 22. The upper side of the diaphragm is exposed to a pressure chamber 23, and the diaphragm is, designed to flex downward with an increase in pressure in the chamber 23. The apparatus is intended to be used in a substantially constant temperature area or designed such that ordinary ambient temperature changes do not inuence its operation. The xed end of the bimetal strip I2 is supported in xed relation to the pressure chamber 23, but in movable relation to the center of exible diaphragm 22.

The parts are so adjusted that the contacts I!! and II just remain open at the minimum pressure to be measured and with the vibrator in operation. Under this condition no current ows in ammeter 2|. Upon an increase in pressure in chamber 23, diaphragm 22 is flexed downward and moves the electromagnet parts 4, 'I, 9 and Ill downward such that contacts I and I I begin to touch as the contact I vibrates away from pole 1. The bimetal I2 has a heater resistance wire 24 about it connected in the circuit of ammeter 2|, and hence an indication is produced and arm |'2 with, its contact I I flexes away from contact I II. The duration of contact per vibratory action of contact Ill thus increases with pressure in chamber 23, and the current passed per cycle increases accordingly. Hence, instrument 2| may be calibrated in pressure. A oneway rectifier 25 is contained in the circuit of coil 8 so that the period of vibration of the armature 9 is once per cycle instead of being twice per cycle. The weight and flexibility of the reed armature 9 should preferably be such as to. have anatural period of vibration near to that corresponding to the forced vibration rate in each case. i

In Fig. 5 the current in the ammeter 2| increases with increase in the pressure to be measured, whereasin Fig. 1 it decreased with rise in temperature to be measured. Also, in Fig. 5 the contact II] moves away from contact Il when the electromagnet is energized, whereas in Fig. 1 the contact III movestoward contact when the electromagnet is energized. In the .casefof Fig. 5 it will be desirable to tune armature 9 to have a somewhat slower natural rate of vibra tion as compared to the electrical vibration rate in order to have the contacts open near the zeror point of the alternating current wave. The advantages of the invention are the' same as those previously mentioned in connection with Fig. 1.

Although the antihunt regulator described is very effective, it costs little and requires little space.

In accordance with the provisions of the patent statutes I have described the principle of oper-.- ation of my invention, together with theapparatus which I now consider to represent the best embodiment thereof, but I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire .to secure by Letters Patent of the United States is:

l. In combination, a measuring detector comprising rst and second cooperating contacts, a bimetal temperature sensitive member for moving the first contact towards and away from the second'` contact in response to the cooling and heating of said bimetal member respectively, electrical connections for causing the electrical heating of said bimetal member when the contacts are closed, Ian electromagnet having a resiliently mounted armature on which said second contact is mounted for moving said second contact towards and away from the first contact', a commercial. source of alternating current supply, independent circuits from said source of supply through'said contacts. and to said electromagnet whereby ,saidv electromagnet is caused to vibrate its armature at a rate proportional to the frequency of such source, said resilient armature being tuned to have a natural rate of vibr-ation different from that of its electrical vibration rate by an amount and in a direction which tends to cause said contacts to open near the zero point of the wave of any alternating current flowing therethrough, and a current indicating instrument in series with the bimetal temperature sensitive member and contacts calibrated in terms of the ambient temperature of said detector, the damping of said instrument in relation to its rate of intermittent energization by reason of the operation of said electromagnet being such as to prevent iiickering of the instrument indication over the temperature measuring range of said apparatus. i,

2. In combination, a measuring detector comprising rst and second cooperating contacts, a bimetal thermal responsive element for moving said first contact towards and away from said second contact as said bimetal member is cooled and heated respectively, means whereby said bimetal member is heated in response to current flow through said contacts when closed, an electromagnet having a resiliently `mounted armature on which said second contact is mounted for moving said second contact towards and away from saidrst contact.V asrsaid electromagnet isr energized-and .deenergized respectively, a source of alternating current supply, electrically inde,-F

therethrough, and a current indicating instru-.

ment in series-with the circuit through saidcon-f tactsicalibrated in terms of the ambient,tempera-r ture ofsaid detector, the damping of said instru-f,

ment-in relation to the Vrate of vibration of said armature being such as to. prevent flickering of the instrument'. indication over the temperature measuring range of said apparatus.

3; In combination, a measuring detector comprisingrst .andvsecond cooperating contacts, a bimetal thermal responsive element for moving thev rst contact towards and away from the second contact in response to cooling and heating of said element respectively, and including electric heater means energized through said contacts when closed,` electromagnetic means for vibrating said'second contact towards and away from the first contact at a constant rate of several times per second such that within the measurement range ofoperation of said detector said contacts open and closeV once for each cycle of operation of'said `vibrating means, and acurrent indicating instrument in series with the bi,

metal thermal response element and contacts.

calibrated in terms of the ambient temperature of said detector, the damping of said instrument in relation to its rate of intermittent energize,-

tion due to the cyclic opening and closing of said,

contacts by saidv electromagnetic means being such as to prevent flickering of the instrument indication over the temperature measuring` range of said apparatus.

4. In combination, a temperature measuring detector comprisinga metallic sealed container, first andsecond cooperating contacts Within said container, a bimetallic thermal responsive element having one endv secured in fixed relation with, an interiory wall of? said,H container; aridi its. other endsupportmg said first. Contact, elettrical. connections from the exterior toI the: 1.1,1'erior Q1? said-container, forming, a circuit: through said contacts when closed; and.` said bimetallic ele:` ment, said .elementl including elegtri heate1- means adapted .to belenergizedthrough said circuitA and when energizedto move therst corn tact away from the second Contactin a dlretiyqn). toopen such'circuit, anelectromagnetic vibrator. supported within saidcontainerandrhaving .a viloratorU armature... membery Which supports Said second contact` such that. the operationof said Vibrator causesthe. opening andiclosing, of said contacts onceper-.operating-cycle of said-vibrator, electrical connections from the exteriorl-to. the interior of said cntainerformingv a circuit in., dependent of said cooperating contacts for en. ergizing said vibrator, said-last-mentioned circuit including` a, magnetic lead-in Wire forming the magneticcoreof Said electromagnetic vibrator, and a current' indicating instrument. in seriesV with. the bimetallic. temperature response ele-.- ment and contacts,calibrated in terms of the ambient temperaturev of said detector, the dampingof ysaid instrument: in relation to its rate. ofenergization by reason` of the cyclic opening and closing of .said contactsbeing vsuch as .to prevent flickering of theinstrument indication over the temperature. measuringrange of said apparatus.

` JOHNVA; ROBERTS.

REFERENCES CITED,

AThe following references are ofk record in the fileof this patent:

UNrTEDsTATEs Plrririyfs` 

